Method for filling a package, particularly a food package

ABSTRACT

The invention relates to a method for filling thin-wall containers including a lid to be opened for use, particularly a can, wherein the container requires an internal pressure to provide a necessary stability in the filled, closed state. The container is tightly closed after filling using a lid to be opened for use and is filled with filling material and a substance used as a pressurizing gas at room temperature before the container is tightly closed. In addition to a solid or liquid first filling material, the container is filled with solid carbon dioxide as a further filling material, wherein the carbon dioxide forms the pressurizing gas after the thin-walled container is tightly closed.

The invention relates to a method for filling thin-wall containersincluding lids to be opened for use, wherein the containers due to theirthin walls require an internal pressure to provide a necessary stabilityin a filled, closed state.

Thin-wall tear up containers of this type are known e.g. as beveragecans. Beverage cans of this type are often filled with carbonatedbeverages and obtain the necessary internal pressure through the carbondioxide included in the beverage. Furthermore it is known e.g. from EP 0906 222 to fill thin-wall containers with a non carbonated beverage andadditionally with liquid nitrogen in order to provide the necessaryinternal pressure after the container is closed.

The containers of this type are closed tight with a lid after filling.The lid has to be opened in order to retrieve the useable content. Atthis moment the positive pressure in the interior of the container islost rapidly. Thus, the inner pressure is used for stabilization duringstorage and transportation and differently from aerosol cans does nothave to be maintained during use.

It has now become apparent that a desirable inner container pressurecannot always be adjusted precisely enough in the known manner.

A method is known from EP 1 686 062 A1, wherein activated charcoal andcarbon dioxide in the form of dry ice pallets are introduced into thecontainer for providing an internal pressure in the container. Thegaseous carbon dioxide released by the dry ice pallets is then partiallyabsorbed by the activated charcoal and released again when the internalpressure of the container drops. The method known from EP 1 686 062 A1apparently has the disadvantage that it is not really suitable for foodcontainers since they should not include any activated charcoal inaddition to the food.

Thus, it is an object of the invention to provide a method whichfacilitates to adjust an inner pressure of a filled closed foodcontainer more precisely.

According to the invention the object is achieved through a method inwhich a thin wall container, e.g. a metal can is initially filled withuseable material as a first filling material and subsequently filledwith solid carbon dioxide, thus dry ice, as another filling material andthe container is eventually closed tight. The dry ice evaporates(sublimates) subsequently already during the filling of the containerand continues to evaporate after the container is closed tight. Theevaporation of the dry ice after tightly closing the containerfacilitates building up a desired internal pressure. The advantage ofusing solid carbon dioxide instead of the known liquid nitrogen is thatthe evaporation rate of the solid carbon dioxide which substantiallydepends from the surface of the solid carbon dioxide is independent fromthe type of filling material. While e.g. a drop of liquid nitrogendistributes over a solid filling material like peanuts or similar andgets a large surface and thus evaporates quickly, the evaporation rateof the dry ice for liquid filling material like e.g. sterilized milk oralso solid filling material like e.g. peanuts is approximately alwaysconstant. This means that the amount of carbon dioxide which evaporatesafter filling in the carbon dioxide and before closing the containertight is in any case substantially similar and in any case sufficientcarbon dioxide remains in the container after the container is closedtight in order to be able to adjust the inner pressure in the tightlyclosed container in a reproducible manner. For liquid filling materialswhich have the capability to absorb carbon dioxide, however, it needs tobe considered that the carbon dioxide which is dissolved in the beverageis not available anymore for providing pressure. Thus, the methodaccording to the invention is suitable in particular for solidmaterials. For liquids particular requirements have to be fulfilled.

Preferably only dry ice is filled into the container as the only fillingmaterial besides the actual useable material, thus the content to bepackaged which is to be sold or transported in the container, before thecontainer is closed.

Preferably the volume of the dry ice filled into the container isbetween 1 g/l and 4 g/l with reference to a gas volume which is computedas a difference between a total volume of the container and the portionof the volume which is filled with a liquid or solid filling material.Such a volume of dry ice yields the desired inner container pressureafter closing the container which is required for preventing the thincylinder section shaped container walls from being crushed.

A preferred method includes e.g. the following method steps:

-   -   Providing a thin wall metal can body;    -   Filling the thin wall metal can body with a filling material;    -   Filling the thin wall metal can body with a defined amount of        dry ice; and    -   Gas tight closing of the thin wall metal can body with a can lid        within 500 seconds at the most after filling the thin wall metal        can body with dry ice.

The preferred method is based on the finding that the sublimation of thedry ice at ambient pressure (1013 hPa) occurs in time frames whichfacilitate performing the gas tight closing of the metal can body within500 seconds after filling with dry ice timely enough so that the desiredhigh internal pressure is subsequently generated through additionalsublimation of the dry ice remaining in the closed can without having tofill too much dry ice into the can. Thus, it is the goal not to havemore than 50% of the dry ice originally filled into the can sublimateuntil the can is closed.

The filling material is preferably a material including particles whichcan also be a food material like e.g. nuts. Under certain conditions,this means considering a possible solubility of carbon dioxide in therespective liquid, the method can also be used for packaging liquids.

The container to be filled through the method is preferably a containerwith a thin wall cylindrical can body made from steel sheet material oraluminum sheet material which includes a total volume of 0.15 l or moreand has a wall thickness at the cylindrical wall section between 0.05 mmand 0.12 mm. The can lid for closing the can body is preferably analuminum lid which is connected gas tight through a gas tight doublefold with the can body after filling the can body. As an alternative toclosing the filled container with a metal cover (e.g. aluminum or tinplate) a closing can also be provided through a pressure tight can lidmade from plastic material. Preferably lids, in particular metal lidsare provided with a scored portion for tearing the lid up during use,thus a so-called tear up lid. Alternatively, however, it is alsopossible to use lids without the scored portion.

The invention shall now be described with reference to an embodimentbased on the drawing FIGURE.

FIG. 1 illustrates various stages of filling a container through themethod according to the invention.

FIG. 1 a illustrates a non-filled can body that is open on the top andmade from thin wall steel or aluminum plate material. A cylindrical wallsection 12 of the can body 10 has a wall thickness between 0.05 mm and0.12 mm;

FIG. 1 b illustrates the can body 10 of FIG. 1 a with a solid or liquidfilling material 14 filled therein. The filling material 14 is a foodand uses a portion 16 of a total volume of the can body 10, so that agas volume 18 remains above the volume portion 16.

FIG. 1 c illustrates that subsequently to filling the can body 10 withfilling material 14 dry ice 20 is filled into the can body 10. At normalambient pressure the dry ice 20 starts to sublimate immediately, so thatthe gas cavity 18 fills with gaseous carbon dioxide.

FIG. 1 d eventually illustrates that the can body 10 is subsequentlyclosed gas tight through a lid 22, before all solid carbon dioxide issublimated. The lid 22 is connected gas tight through a double fold 24with the can body 10. After closing the container gas tight theconversion of the remaining solid carbon dioxide 20 into gaseous carbondioxide continues and provides that the interior container pressureeventually reaches the desired level which is required for stabilizingits thin cylindrical walls. A suitable amount of solid carbon dioxidewith reference to the gas volume is between 1 g/l gas volume and 4 g/lgas volume. The lid 22 is preferably applied within 500 seconds afterfilling the solid carbon dioxide into the can body 10.

1. A method for filling a thin wall container including a lid that is tobe opened for use, in particular a metal can, wherein the containerrequires an internal pressure in filled closed condition for providing anecessary stability, wherein the container is closed tight after fillingthrough a lid that is configured to be opened for use, wherein thecontainer is filled with filling material and a material that serves asa pressure gas at ambient temperature before being closed tight, andwherein solid carbon dioxide is filled into the container as anadditional filling material besides a solid or liquid first fillingmaterial, wherein the carbon dioxide forms the pressure gas after tightclosure of the thin-walled container.
 2. The method according to claim1, wherein the container is filled with a first filling material that isliquid or solid at room temperature, wherein the first filling materialfills a portion of the total volume of the container so that a gasvolume remains defined as a difference between total volume and volumeof the first filling material, wherein a volume of dry ice withreference to the gas volume is between 1 g/l and 4 g/l.
 3. The methodaccording to claim 1, further including the following steps: providingof a thin-wall metal can body, filling the thin-wall metal can body witha first filling material, filling of a thin-walled metal can body with adefined volume of dry ice, and closing the thin-walled metal can bodygas-tight with a can lid within a maximum of 500 seconds after thefilling the thin-wall metal can body with dry ice.
 4. The methodaccording to claim 1, wherein the filling material is a food material.5. The method according to claim 1, wherein the container to be filledincludes a thin-wall, cylindrical can body made from steel- or aluminumsheet material, which includes a total volume of more than 0.2 l and hasa wall thickness between 0.05 mm and 0.12 mm at its cylindrical wallsection.
 6. The method according to claim 1, wherein the container isclosed airtight with a tear open lid after the container is filled. 7.The method according to claim 1, wherein the method is performed underan inert gas atmosphere.